1. Field of the Invention
The present invention relates to a strip of webbing which is employed in seat belts for vehicle, aircraft, or the like.
2. Description of the Related Art
A 3-point seat belt has been widely used in conventional vehicles. As illustrated in FIG. 1, in the 3-point seat belt, a strip of webbing 6 is fixed at 3 points, e.g., at a fixture 1, at a buckle 3 connected with a slipping guide 2 into which the webbing 6 is inserted, and at an upper slipping guide 4, in order to support the body of a passenger seated thereon.
When the 3-point seat belt is unfastened, a force is always exerted to the webbing 6 by a retractor 5 in a direction of taking up the webbing 6 in order to remove the looseness therein. Hence, when the slipping guide 2 into which the webbing 6 is inserted, and the buckle 3 are disengaged, the webbing 6 is taken up and accommodated in the retractor 5 until it exhibits no excessive looseness. On the other hand, when the 3-point seat belt is fastened, the webbing 6 is taken out by a necessary length by exerting an opposing force against the taking up force associated with the retractor 5.
Thus, every time the 3-point seat belt is fastened or unfastened, the webbing 6 is taken out and taken up repeatedly. Accordingly, the through hole 7 of the upper slipping guide 4 and the surface of the webbing 6 are rubbed each other with a high frequency.
Conventionally, a mixture of polyurethane resin and silicone is adhered to the surface of the webbing 6 so as to reduce the wear which results from the rubbing against the through hole 7 of the upper slipping guide 4. Namely, the mixture is adhered to the webbing 6 in order to enhance the smoothness of the webbing 6 (i.e., the accommodatability of the webbing 6), and at the same time to prevent the webbing 6 from wearing.
In general, it has been a well known technique that the silicone, or the like, is coated on cloth in order to improve the smoothness. However, the webbing 6 for the seat belts is made from multi-filament threads, and the multi-filament threads are made from synthetic fiber which have a smooth surface. Accordingly, it is hard to adhere and keep the silicone itself on the surface of the webbing 6. Hence, the polyurethane resin which exhibits an adhesive property to the webbing 6 and an anti-wear property is mixed with the silicone, thereby adhering the silicone on the surface of the webbing 6.
Although the mixture of the polyurethane resin and the silicone is good in the anti-wear property, it is insufficient in the light resistance. Namely, when the mixture is exposed to light for a long period of time, it undergoes the photodissociation and thereby it is more likely to come off from the surface of the webbing 6. Specifically speaking, the more the accumulated time of the exposition of the webbing 6 to the solar light is, namely the longer the webbing 6 is irradiated by the solar light, the more the polyurethane resin, holding the silicone on the surface of the webbing 6, is likely to be degraded and dissociated by the solar light. Accordingly, the polyurethane resin can scarcely hold the silicone thereon, and the silicone comes off from the surface of the webbing 6 gradually. As a result, the smoothness of the webbing 6 is reduced, and the anti-wear property is also deteriorated.
When the smoothness of the webbing 6 is lost, the resistance is increased during the retraction of the webbing 6 into the retractor 5. Consequently, it takes longer to take up the webbing 6 by the same length, and it also requires to exert a lager force while pulling out the webbing 6. Thus, there might arise a fear that the seat belt cannot be fastened or unfastened smoothly.